Navigation devices are known from the related art, in which a part of a roadmap is represented on a screen as a function of the position of a vehicle and its direction of motion. In this context, different types of representation are customary, which can be divided into different categories with respect to the data structures on which they are based and the computing operations carried out by the system. The simplest model is a two-dimensional representation of a vector map containing the navigational data (surfaces, lines, dots, labels). In order to provide the driver of the vehicle with visual information about his environment that is as easy to interpret as possible, by contrast, a perspectival representation of the map data is often preferred. Optionally, the representation in this instance may contain elevation information about the not necessarily flat terrain or may merely be a three-dimensional representation of a “flat” map. The latter model is called a pseudo-3D representation. In both cases, the data of a vector map on which the map is based must be converted under the influence of a coordinate transformation into the image data containing a perspectival representation. Usually, a linear mapping specification is used, in which for lines existing in the map simply their end points are projected and in turn connected to a line. These lines then form polygons that must be filled. A standard CPU (central processing unit) or a GPU (graphical processing unit) executes the required 3D vector operations and polygon shadings in hardware.
The perspectival impression is achieved by choosing a virtual viewing position above the actual vehicle position. The higher the viewing position, the more information is presented to the user, which he would possibly not receive from his position in his vehicle. Often, the position of the vehicle is also represented on the map for better orientation.
In principle, any projection method that produces a spatial effect may be used for computing the image data. Particularly well-known in this context is the central projection, in which all points to be represented on the map are connected via connecting lines to a projection center, which coincides with the viewing position, the intersections between the connecting lines and a projection plane yielding the projected image. Due to the geometry of such or similar projections, a horizon appears in the visual representation, in the proximity of which the roads, fill areas etc. appear densely packed. The visual representation both in this area as well as in an area above the horizon, representing the air space, which often contains only decorative textures, contains only little information that is useful to the user of the navigation device.